1. Field of the Invention
The invention relates to apparatus and methods for administering measured doses and particularly, but not exclusively, to apparatus and methods for automatically, accurately and quickly dispensing and administering measured liquid volumes from injectors. The invention has particular utility for veterinary purposes such as the needless, hypodermic dosing of animals with liquid medicaments. The invention is especially useful in slap injectors designed to dose animals of free range. However, it will be appreciated from the following description that the invention is not limited to such applications and may be used for many other purposes where it is necessary to quickly and accurately dispense repeated, measured volumes of a liquid.
2. Background Information
The state of the art generally includes various devices and methods for automatically dispensing and administering measured volumes of fluid into animals. For example, a common device is a hand-held injection gun that has a projecting needle and a trigger mechanism. The needle is introduced into the body of the animal and the trigger mechanism is squeezed to actuate a syringe-like device that delivers the injectate along the hollow needle and into the animal. While such injection guns are effective where the animal is closely restrained and comparatively still, they may be difficult to operate with comparatively unrestrained animals or with animals of free range because it is difficult to synchronize the operation of the trigger with the insertion of the needle in the animal. In order to overcome this problem, slap injectors have been designed to be slapped or prodded against the body of an animal. The impact of the device against the animal automatically projects a hollow needle through the animal's skin and triggers a discharge of a measured dose of injectate through the needle. The slap injector may have a straight-on design wherein the needle and handle are aligned and the slap injector is thrust into the animal to trigger the discharge, or the slap injector may have an angled design wherein the needle and handle form an angle, preferably a 90.degree. angle, and the slap injector is swung in a hammer-like motion into contact with the animal.
An example of an angled slap injector is disclosed in British Patent No. 2288539 entitled Slap Injector, and is hereby incorporated by reference. The slap injector generally comprises a handle, a body part, a syringe device, operating means, a trigger device, and actuating means. The body part is mounted to one end of the handle. A hollow needle projects from the body part. The actuation means is mounted on the body part and actuates the trigger device, which upon engagement with an animal, controls the operating means. In use, the handle is swung so that the actuating means engages the body of the animal being injected and is displaced relative to the body part of the device as the needle passes into the body of the animal. The displaced actuating means actuates the trigger device, and the actuated trigger device permits the operating means to discharge the syringe device. Preferably return means return the actuating means to its initial position relative to the body part after the syringe device is discharged and automatically withdraws the needle from the body of the animal. The return means may comprise first spring means arranged to oppose the initial movement of the actuating means relative to the body part and to return the actuating means to its initial position after the discharge of the syringe device. The actuating means may include a slap plate extending transversely to the hollow needle. The needle projects through an aperture in the slap plate as it is displaced relative to the body part. The apertured slap plate guides and supports the needle as it is inserted into the animal, thus reducing the risk of bending the needle. The outer surface of the slap plate is preferably convexly curved with the needle aperture located at the lowermost point of the curve. This design allows the fill length of the needle to pass into the animal even if the device is not applied perfectly squarely to the animal's hide. The actuating means may also include a peripheral wall which surrounds and shields the needle when the actuating means is in its initial position. The operating means for discharging the syringe device may comprise an operating element and second spring means for displacing the operating element from a cocked position in which the spring means is stressed to an extended position in which the spring means is released. The operating element is held in the cocked position by the trigger device, and is operatively coupled to discharge the syringe device as it moves to the extended position. Preferably the operating element and second spring means extend longitudinally with respect to the handle of the injecting device.
Slap injectors are generally effective, but may encounter problems while dosing an animal. One potential problem is that the needle may bend and harm the animal. Another problem is that inaccurate or inconsistent dosages may be delivered because the slap injector was not in operational contact with the animal for a period of time long enough to fully discharge the desired dose into the animal.
Applicants' invention provides an injector pump which can be incorporated into a new and improved design of a slap injector. Specifically, applicants' invention is a high-pressure pump of flexible design that quickly and repeatably delivers an accurate measured volume under high pressure into an animal with or without a needle.